As one of systems for detecting a fire (e.g., a forest fire) at an early stage in order to minimize the damages caused by the fire, there has been known a system for detecting a hot portion (heat source) from an image generated by an infrared camera.
As other systems for detecting a forest fire, there has been known, for example, a system for detecting a smoke from a visible light image, or a system for detecting a smoke from an image captured by a camera mounted on a satellite.
As one of systems for detecting a fire using a camera, there has been known a system that captures an image of a place where a fire has occurred using a television camera, when it is determined that the fire has occurred based on data of detectors that detects, for example, a smoke concentration or temperature.
As one of fire detectors for detecting an occurrence of a fire on the basis of presence or absence of a smoke caused by the fire, there has been known a fire detector which combines a photoelectric or ionization smoke detector with a CO2 sensor in order to reduce a false alarm.
In addition, as one of methods for detecting a fire at an early stage, there has been known a method in which two types of detectors each having different signs of a fire to be detected are used to determine whether or not a fire has occurred, based on the detection results of the two types of detectors.
Related techniques are disclosed in, for example, Japanese Laid-Open Patent Publication No. 07-254096, Japanese National Publication of International Patent Application No. 2000-504132, and Japanese National Publication of International Patent Application No. 2000-516000.
The temperature of an object existing within an image capturing range may be identified from an infrared camera image. However, it may not be possible to identify the reason why and how a hot portion reaches a high temperature An object existing within an image capturing range may become a high temperature due to, for example, a temperature rise by the sunshine as well as the heat from a fire. Therefore, a fire ranger has to always monitor the images of the infrared camera to check the presence of a fire occurrence.
In addition, when a smoke is detected from a visible light image, it is difficult to determine whether the smoke is caused by a fire or a temporary smoke caused by other reasons.
Further, in a case where an infrared camera or a visible light camera is used to detect a fire occurring in a wide range such as, for example, in the mountains, there is a need to install a great number of cameras throughout the wide range, which results in an increase in installation costs.